What does the word "more" refer to: "cars and trucks" or "efficient")?

Question

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More efficient use of fuels, mainly through more efficient cars and trucks, accounts for almost 36% of the emission saved.

(does it mean: more efficient or more cards and trucks?)

Answer 1

It is formally ambiguous, but not in the way you think.

1) (More efficient) (cars and trucks) where more modifies 'efficient'. Make all cars and trucks more efficient

2) More (efficient cars and trucks) where more modifies 'efficient cars and trucks'. Make more of only the efficient cars and trucks

There is no possible reading where 'more' modifies 'cars and trucks' without including 'efficient' in the mix